I'm sure they do. Professional criminals aren't desperate and simple-minded. Someone willing to risk running up and swiping a camera (or hell, a lens) right off someone isn't going to spring for a t3i or an 18-55 kit. They're going to know to look for the big 800 or 5D or that little red dot, and the big, heavy looking piece of glass with the blue badge on the side or the red ring around the tip.

EDIT: And I'm not saying this to suggest that London (or most other cities) are some manner of criminal/camera death trap. My point is that there are several subtle signs that people can be trained to look for, and that it would be totally prudent and easy to cover up. (This strategy has been taken to the extreme by that guy who disguised his x100s to look about a hundred years old. If anybody has that picture, I couldn't find it)